TOPIC 3.0 CONVERTING ELECTRICITY

AND EFFICIENCY

I. Forms and Transformations Energy – the ability to do workA. Forms of Energy1) Chemical energy – potential energy

that is released when chemicals reactEx. Food, batteries

2) Electrical energy – energy of electron flow (transfer)Ex. electrical circuits

I. Forms and Transformations

A. Forms of Energy3) Mechanical energy – energy of an

object because of its motion, or potential to move.

Ex. An elastic has the potential to move when pulled back; when moving has motion

4) Thermal energy – the kinetic energy of a particle in an object; the faster it moves the more kinetic energy is present (the hotter the temperature)

I. Forms and TransformationsB. TransformationsPredict the input (starting) and output

(ending) energy for each converting device:

a) Toasterb) Batteriesc) Flashlightd) Blender

I. Forms and TransformationsB. Transformationse) Radiof) TVg) Human bodyh) Explosives

I. Forms and Transformations Thermocouple – a device that

converts thermal energy to electrical energy Made of two different metals that heat

(conduct) at different rates Produces electricity

DEMO: Transforming Heat into Electricity

Pg. 322 Record any changes in the voltmeter

when a thermocouple is changed from ice water to boiled water

II. Electrical and Mechanical Energy Transformations

A. Famous Discoveries:1) Oersted : A wire with current

produces a magnetic field (deflects a compass)

-Oersted video2) Michael Faraday: Moving a magnet

through coiled wire causes an electrical current (electromagnetic induction)

*These discoveries led to the motor!Faraday simulation

II. Electrical and Mechanical Energy Transformations

B. How a Motor Works Electromagnet – a magnet made by

wrapping wire (with current) around an iron core

B. How a Motor Works Parts to a motor:1) Commutator – a split ring breaks

the flow of electricity for a moment and reverses the current

2) Brushes – contact the commutator and are connected to a battery

B. How a Motor Works Parts to a motor: 3) Armature – a rotating shaft to

which the wire is attached (electromagnet)

>this continues to spin due to momentum

Motor #2 Video

brushes

magnets

commutator

Armature (contains wire)

Connect to battery

Parts of a MotorParts Function

Spins due to changing current in wire and interaction with magnetsMakes light contact with split-ring

Causes current to reverse direction every half turnCause attraction of opposite poles and repel of like poles

II. Electrical and Mechanical Energy TransformationsB. How a Motor Works

1. Electromagnet (with running current) is placed between the poles of a permanent magnet.

2. The brushes bring current from the power sources to the commutator – is then transferred to armature.

3. Electromagnet (armature) turns to align N of armature to S of magnet (opposite attract)

4. Just as the armature aligns with the magnet, the commutator reverses the current in the electromagnet Causes the poles of the electromagnet

(armature) to reverse 5. The armature gets attracted to

opposite pole and continues to spin (creates mechanical energy)

II. Electrical and Mechanical Energy TransformationsC. Types of Current1) Direct current

(DC) – electricity flows only in one directionEx. Current from batteries – iPod, cell

(Edison)

II. Electrical and Mechanical Energy Transformations

C. Types of Current2) Alternating current

(AC) – electricity that flips direction 60 times per secondEx. Currents from outlets

(Tesla)AC vs DC Video

II. Electrical and Mechanical Energy Transformations

D. Transporting Current Power companies transport electrical

current as: High voltage (50 000V) AC currentto reduce energy loss

However, the voltage must be reduced to use in homes (120V) – done with a transformer

II. Electrical and Mechanical Energy Transformations

D. Transformation of VoltageTransformers – used to increase or

decrease voltage; The current is fed into the primary coil

which “induces” (causes) a current in the secondary coil

D. Transformation of Voltagea) Step-up – increases voltage - primary coil has less coils than

secondary coil

b) Step-down – decreases voltage -primary coil has more coils than

secondary coil

Ex. Would a power company use a step up or step down generator to increase the voltage for transportation of current?

b) Would the secondary coil have less or more coils than the primary?

II. Electrical and Mechanical Energy Transformations

E. Generating Electricityo Motors use current electricity

(created by magnetism) to create mechanical energy. (Oersted’s idea)

o Generators take mechanical energy and create electrical energy by using electromagnetic induction (Faraday’s idea)

Device Starting Energy

Ending Energy

Scientist associated

Other Notes

Motor Electrical Mechanical

Oersted -current carrying wire produces a magnetic field which causes motor to turn

DC generator

Mechanical

Electrical Faraday (electromagnetic induction)

-a wire moving through a magnetic field produces current-uses 1 split ring commutator

AC generator

Mechanical

Electrical same as DC generator

-uses a ring of wire that causes alternating currents to be produced (e-flow in both directions)

E. Generating Electricity To increase the amount of energy

produced you can: 1. Increase the speed of rotation. 2. Increase the strength of the

magnet 3. Increase the number of coils

III. Energy Input/Output

A. Measurements 1. Power – the rate at which a device

converts energy Measured in watts (W or J/s) The larger the conversion, the larger the

power rating

III. Energy Input/Output

Ex. If a lightbulb is 60W it converts how many Joules of energy per second?

What is the energy conversion?

III. Energy Input/Output

The formula for power is:

P = I V

P – power (W) I- current (A) V – voltage (V)

Ex. What current does a 60W bulb require using 120V?

Ex. How much power does a lamp with two 60W bulbs require using a 120V socket?

III. Energy Input/Output

A. Measurements2. Energy

E = Pt

E –energy [J]P – power [W]t – time [s]

A. Measurements 2. Energy

Converting hours to seconds: x 3600 Converting mins to seconds : x 60

III. Energy Input/Output Ex. How much energy is consumed

by a laptop that uses 90W of power and is left on for 8 hours?

III. Energy Input/Output

Kilowatt hours is another unit for Energy

E = P x t = kW x h = kWh

III. Energy Input/Output

a) How much energy does a 1000W oven use in 3 hours of baking?

b) If it cost $0.0225/ kWh for energy, how much did it cost to run the oven?

III. Energy Input/OutputB. Law Conservation of Energy Appliances usually have listed an

“efficiency” rating . This communicates how much energy needed is actually used “usefully”.

Ex. A tungsten lightbulb is only 5% efficient. Where does the other 95% of energy

not used “usefully” go?

III. Energy Input/OutputB. Law Conservation of Energy This law states that:“Energy cannot be created nor

destroyed, only converted to other forms (waste)”

What energy forms are “useful” for a lightbulb?

What form of energy is the rest converted to?

III. Energy Input/OutputB. Law Conservation of Energy

KEY IDEA:

Energy not used usefully is MAINLY converted to thermal energy!

III. Energy Input/OutputB. Law Conservation of EnergyEx. For each of the following devices,

list the “useful” and “waste” energy:a) Motor – useful:

- waste:b) Muscles – useful:

- waste:c) TV – useful:

-waste:

III. Energy Input/OutputC. Efficiencyo Is how much of the “input” energy is

converted to “useful output”

%Efficiency = useful output x 100%

input

Ex. Calculate how efficient a toaster is if it uses 1350J and only 1000J is converted to heat.

Skill Practice pg. 336

III. Energy Input/Output

D. Limits to Efficiencyo Rarely are devices 100% efficiento Anytime parts are moving, friction

results in a conversion of useful energy to heat energy (waste)

III. Energy Input/Output

D. Limits to Efficiencyo How can we increase efficiency of

appliances?

Apply lubricants (oil) to reduce friction

Apply insulation (reduce heat loss)